The downside is that all these new cyclists (or many of them, anyway) don't know the rules of the road. Twice, I almost got hit by a car while on my bike commute last week as a result of other cyclists doing the WRONG thing. If I hadn't been anticipating that those cyclists were going to make those stupid moves (and what the resulting things the cars would do), I'd be out of commission right now.

I'm afraid a potential increase in bicycle related accidents/deaths is going to hurt our cause if new riders don't take the time to educate themselves.